PHYLOGENETIC-RELATIONSHIPS BETWEEN SOME MEMBERS OF THE GENERA DELEYA,HALOMONAS, AND HALOVIBRIO

The genera Halomonas and Deleya, which constitute the family Halomonad aceae, are difficult to differentiate on the basis of phenotypic and c hemotaxonomic attributes. DNA-rRNA hybridization studies have indicate d that some Halomonas spp. have the same level of relationship to the type species of the genus Deleya as some Deleya spp. A phylogenetic an alysis of the 16S rRNA sequences of seven members of the Halomonadacea e indicated that the members of the genera Halomonas and Deleya do not form separate monophyletic subgroups, confirming the lack of any phyl ogenetic support for retention of these taxa as separate genera. A phy logenetic analysis of the 16S rRNA sequence of Halovibrio variabilis c onfirmed that this species belongs in the Halomonadaceae. All of the m embers of the Halomonadaceae examined and Halovibrio variabilis posses s a cytosine residue at position 486 (Escherichia coli numbering), whi ch is an extremely rare attribute among the prokaryotes and has been r eported in only one other species, Listonella anguillarum. Several oth er signature characteristics which define this group in the gamma subc lass of the Proteobacteria are identified. The Jukes-Cantor distances between members of the family Halomonadaceae, including Halovibrio var iabilis, range from 0.086 to 0.000 (the levels of similarity between t he 16S rRNA sequences range from 92.6 to 100%). The members of the gen era Halomonas, Deleya, and Halovibrio form a monophyletic group and sh are common chemotaxonomic and phenotypic characteristics. Subgroups co ntaining members of the genera Halomonas, Dekya, and Halovibrio cannot be resolved on the basis of phylogenetic, chemotaxonomic, or phenotyp ic data. Our data indicate that the members of the genera Halomonas, D eleya, and Halovibrio should be united in a single genus.